Re: [PATCH 1/2] RDMA/umem: Change for rdma devices has not dma device

[Leon Romanovsky <leon@kernel.org>]

On Wed, Mar 25, 2026 at 10:27:38PM -0700, Zhu Yanjun wrote:
> Current implementation requires a dma device for RDMA driver to use
> dma-buf memory space as RDMA buffer.
> 
> Signed-off-by: Zhu Yanjun <yanjun.zhu@linux.dev>
> ---
>  drivers/infiniband/core/umem_dmabuf.c | 35 ++++++++++++++++++++++++++-
>  include/rdma/ib_umem.h                |  1 +
>  2 files changed, 35 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/infiniband/core/umem_dmabuf.c b/drivers/infiniband/core/umem_dmabuf.c
> index d30f24b90bca..65c5f09f380f 100644
> --- a/drivers/infiniband/core/umem_dmabuf.c
> +++ b/drivers/infiniband/core/umem_dmabuf.c
> @@ -142,6 +142,8 @@ ib_umem_dmabuf_get_with_dma_device(struct ib_device *device,
>  		goto out_release_dmabuf;
>  	}
>  
> +	umem_dmabuf->dmabuf = dmabuf;
> +
>  	umem = &umem_dmabuf->umem;
>  	umem->ibdev = device;
>  	umem->length = size;
> @@ -152,6 +154,24 @@ ib_umem_dmabuf_get_with_dma_device(struct ib_device *device,
>  	if (!ib_umem_num_pages(umem))
>  		goto out_free_umem;
>  
> +	/* Software RDMA drivers has not dma device. Just get dmabuf from fd */
> +	if (!device->dma_device) {

I understand your intent, but RXE cannot support dmabuf, as dmabuf
requires a real DMA‑capable device to be attached. In addition, it is
unclear how you expect PCI peer‑to‑peer operations to work when one
side (RXE) is not a PCI device at all.

Thanks